American troops had landed on the Philippine island of Leyte. The Japanese had long realized that the loss of the Philippines would cut Japan off from access to crucial resources (particularly oil) in South-East Asia.
The Japanese high command had developed a plan: Send a decoy fleet as bait to draw the main American fleet away from the island. This decoy fleet was to be sacrificed while a second Japanese fleet, made up of battleships, would destroy the US vessels supporting the landing force thus halting the American invasion of the Philippines.
The bait was tempting: The Japanese decoy fleet was mostly aircraft carriers, including the well known fleet carrier Zuikaku, some light carriers, and some battleships that had been converted to carriers. (The Japanese were willing to lose their carriers since there were no longer the aircraft or aircrews to equip the carrier fleet.)
The Japanese battleship fleet comprised 7 battleships, including the giant Yamato and Musashi, with their 18-inch guns, (plus 11 heavy cruisers).
Ironically, the battleship fleet is spotted before the decoy fleet and the Americans attack and sink the Musashi. On 25 October, the decoy fleet is spotted and the Zuikaku is sunk.
By the end of the battle, the Americans had lost one light carrier and two escort carriers. The Japanese had lost one fleet carrier, three light carriers, and three battleships. It was now inevitable that Japan would lose the Philippines and so future access to its source of oil.